Abstract The goal of this Fast track application is to develop a non-invasive diagnostic test (based on MUC4 and MUC16 mucins) that can serve as an adjunct to cytological analysis of fine needle aspirates (FNAs) for accurate prediction of malignancy in patients with cystic pancreatic lesions. Due to asymptomatic nature and lack of methods for early detection, > 80% of pancreatic cancer (PC) patients present with an unresectable primary tumor with distant metastasis at the time of diagnosis. While the overall 5 year survival rate of pancreatic cancer is dismal, signi?cantly better outcomes have been reported for smaller tumors detected at an earlier stage. Slow development of PC in conjunction with the better curative response of patients with early disease underscore the need of early detection of pancreatic cancer. Pancreatic cystic lesions, earlier considered to be rare, are increasingly being recognized due to increased number of individuals being subjected to diagnostic imaging; however, their exact prevalence is unknown. These cystic pancreatic lesions have variable malignant potential: while mucinous cystic neoplasms (MCNs) and intraductal pancreatic mucinous neoplasms (IPMNs) have a high probability of developing into malignant lesions, serous cystic neoplasms (SCNs) are considered benign. Despite the critical need, accurate discrimination between high- and low-risk cystic lesions is challenging due to their symptomatic and radiographic similarities. Although cytologic examination of endoscopic ultrasound (EUS) guided fine needle aspirates (FNAs) has emerged as an indispensable part of presurgical evaluation, in practice, 50%?60% of such analyses are inconclusive and unreliable in discriminating between serous and mucinous lesions. Using anti-MUC4 MAb 8G7 generated by our group several studies have established that cell surface mucin MUC4 is promising prognostic and diagnostic biomarker. Further MUC4 and MUC16 exhibited 100% specificity for malignancy in EUS-FNAs containing atypical ductal epithelial cells. The central hypothesis of this proposal Detection of MUC4 and/or MUC16 in pancreatic tissues (EUS FNAs) is positively correlated with the presence of already existing pancreatic cancer or cystic lesions with malignant potential and thus MUC4/16 staining is a powerful tool for the accurate prediction of malignancy and pre-surgical stratification of patients with cystic lesions of the pancreas. Studies proposed for Phase I will result in the development of a prototype kit for MUC4MUC16 IHC (Aim 1) and provide proof of concept in support of the aforementioned hypothesis. Studies proposed in Phase II will validate the significance of MUC4/16 immunostaining in a blinded trial and determine how MUC4/16 expression correlates with the clinical outcome of the solid/cystic pancreatic diseases (Aim 2). Further, we propose to test the prototype kit in a clinical setting (CLIA Lab) to validate performance (Aim 3). Overall, the proposal will lead to the development of a clinical test to stratify patients for surgical intervention or surveillance in the context of pancreatic cystic lesions and PC.